Numerical investigation of the effects of tunnelling on existing tunnels

Abstract

Construction of the Crossrail tunnels just beneath the existing Central line tunnels at the northern side of Hyde Park provided the impetus for this paper. A basic three-dimensional (3D) finite-element (FE) model was developed to study a general case of a new tunnel (NT) crossing perpendicularly below an existing tunnel (ET). A series of 3D FE analyses was carried out and the results presented in this paper reveal some of the interaction effects. Changes in hoop forces, bending moments and lining deformations of the ET due to excavation of the NT are discussed. Conclusions are drawn about how the relative position of the excavation face of the NT in relation to the ET's axis affects the latter's behaviour. Cross-sectional and longitudinal deformations of the ET are discussed, leading to recommendations for field monitoring of similar interaction cases. Two parametric studies were also carried out to quantify the effects of the magnitude of the earth pressure balance machine face pressure and the longitudinal stiffness of the ET on the predicted behaviour of the ET due to construction of the NT.